1. Field of Invention
The present invention relates to a lumbar support device for use in an automotive seat.
2. Description of Prior Art
There has been known such a typical rotary type of lumbar support device as disclosed from the Japanese U.M. Laid-Open Pub. No. 3-120848 in the field of vehicle or automotive seats. FIG. 1 shows this sort of lumbar support device, which includes basic major elements: a motor (26'), a threaded rotary adjustment mechanism (16', 18'), an arm (14') and a lumbar plate (12'). The motor (26') is provided with a reduction gear (26'a) from which a threaded spindle (16') projects to engage a nut member (18') threadedly, constituting that threaded rotatry adjustment mechanism. The arm (14') is fixed at one base end portion thereof to the nut member (18') and has an outwardly extension (14b') formed therefrom. The outwardly extension (14b') is rotatably supported in a bracket (20') fixed on the motor (26'), forming a center of rotation of the arm (14'). Another free end portion (14'a) of the arm (14') is connected to the central part of the lumbar plate (12') in a rotatable manner. Thus, operation of the motor (26') causes vertical motion of the nut member (18') along the threaded spindle (16') to rotate the lumbar plate (12') relative to the arm end extension (14'b). Since the lumbar support device is provided within a seat back of automotive seat at a point corresponding to the lumbar part of an occupant on the seat, the lumbar plate (2) is rotatively displaced in the direction forwardly and backwardly of the seat back.
However, in this conventional lumbar plate device, the free end (14'a) of the arm (14') is simply rotated relative to the center (14'b) of rotation, and thus displaced on an arcuate path. As indicated by the arcuate arrow in FIG. 1, such mere circular rotation of the arm (14') or its free end (14'a) in the direction from the horizontal position (1) to an upward position (2) or vice versa results in the lumbar plate (12) being displaced laterally by an amount of "D". This has been found defective in varying the lumbar support point in the width-wise direction of seat back and making an occupant on the seat uneasy and unpleasant at his or her lumbar part, which deteriorates the fatigue alleviation effects of the lumbar plate (12').